Hmm. Having read your post, surely the bug is having a function where set(foo, false) removes foo entirely. What if you want foo to have the value False?

Hmm. Having read your post, surely the bug is having a function where set(foo, false) removes foo entirely. What if you want foo to have the value False? Even besides the unintended behaviour where 0 is coerced to a boolean value, this function seems poorly designed.